1. Field of the Invention
The present invention relates to a stable composition of water-soluble organosiloxanes obtained by
a) reacting a water-soluble amino-functional alkoxysilane with at least one water-insoluble alkoxysilane PA1 b) by adding water and, optionally, an organic or inorganic acid, to form a mixture, and PA1 c) removing the alcohol formed during step b) from the mixture, PA1 a) a water-soluble amino-functional alkoxysilane with at least one water-insoluble alkenyl-functional alkoxysilane PA1 b) by adding water and, optionally, adding an organic or inorganic acid, to form a mixture, and PA1 c) removing the alcohol formed in the reaction from the mixture, PA1 a) a water-soluble amino-functional alkoxysilane with at least one water-insoluble alkenyl-functional alkoxysilane PA1 b) by adding water and, optionally, adding an organic or inorganic acid, to form a mixture, and PA1 c) removing the alcohol formed in the reaction from the mixture, PA1 a) a water-soluble amino-functional alkoxysilane, preferably a 3-aminopropyltrialkoxysilane, with at least one water-insoluble alkenyl-functional alkoxysilane, preferably a vinyltrialkoxysilane, PA1 b) by adding water to form a mixture, and PA1 c) removing the alcohol formed during step b) from the mixture, to wherein the amino-functional alkoxysilane and the water are used in the reaction at least in amounts such that all of the alkoxy groups of the water-insoluble alkenyl-functional silane can react, and wherein the composition has a pH of from 2 to 6, preferably a pH of from 3 to 5, particularly preferably a pH of from 3.5 to 5, very particularly preferably a pH of from 3.5 to 4.5. The pH is preferably adjusted before or during the reaction or both by adding an organic or inorganic optionally aqueous, acid, preferably formic acid, acetic acid, HCl, HNO.sub.3 or H.sub.2 SO.sub.4. The composition is especially useful to improve the processing conditions during the silanization of a filler, in which case a mixture of filler (e.g. aluminum hydroxide), water and the composition of the invention exhibits a significant drop in viscosity while being stirred after just a few minutes, so that the starting paste can be conveyed in a low-viscosity state easily and in a simple and economic manner via a pump, for example to a spray dryer.
wherein the amino-functional alkoxysilane and the water are present in the reaction at least in amounts such that all of the alkoxy groups of the water-insoluble silane can react and such that when the resulting composition is diluted with water, essentially no alcohol is liberated by hydrolysis, and also to a process for its preparation and to its use.
2. Discussion of the Background
Compositions of water-based organopolysiloxanes usually contain completely hydrolyzed and oligomerized units: the alkoxy groups of the organoalkoxysilanes used in the synthesis being virtually completely substituted by OH groups. Such water-based organopolysiloxane-containing systems becoming widely used since they are essentially free from solvents and they liberate virtually no alcohols by hydrolysis even when diluted with water and upon application. EP-A 0 716 127 and EP-A 0 716 128 discloses water-based organopolysiloxane-containing compositions which are prepared by hydrolytically oligomerizing a "carrier silane", a water-soluble aminoalkoxysilane and water-insoluble alkylalkoxysilanes and ureidoalkoxysilanes in a pH ranging from 1 to 11, and removing most of the alcohol formed in the reaction from the reaction mixture.
The above compositions are usually clear liquids having a long shelf life and a flash point of more than 70.degree. C., and they are widely used, inter alia for improving the rheological properties of polymer dispersions and emulsions and for silanizing surfaces. However, adjusting the rheological properties and modifying surface properties requires an agent specifically matched to the product to be modified. Thus, the as yet unpublished German patent application No. 196 39 782.0 discloses water-based amino-, glycidyl ether-, acrylic- and methacrylic-functional organopolysiloxane-containing compositions.
In addition, EP 0 675 128 A1 discloses a process for the preparation of a stable composition of water-soluble organosiloxanes which includes reacting a water-soluble amino-functional alkoxysilane with a water insoluble vinyl-functional alkoxysilane with the addition of water, and removing the alcohol formed in this reaction from the mixture, wherein the aminofunctional alkoxysilane and the water are used in the reaction in amounts such that all of the alkoxy groups of the water-insoluble silane can react, so that when the resulting composition is diluted with water, essentially no alcohol is liberated by hydrolysis.
Such compositions of water-soluble organosiloxanes are used commercially, inter alia as adhesion promoters in compounds, and fillers and pigments are silanized in mostly complex processes. It is frequently necessary, however, to dry surface-modified fillers on a tray and then to comminute them again by energy-intensive measures. The use of spray-drying as a alternative for tray-drying requires a pumpable composition, and it is frequently necessary to add large amounts of processing auxiliaries to adjust the rheology.